Penning collisions between supersonically expanded metastable He atoms and laser-cooled Li atoms.

We describe an experimental setup comprised of a discharge source for supersonic beams of metastable He atoms and a magneto-optical trap (MOT) for ultracold Li atoms that makes it possible to study Penning ionization and associative ionization processes at high ion count rates. The cationic reaction products are analyzed using a novel ion detection scheme which allows for mass selection, a high ion extraction efficiency, and a good collision-energy resolution. The influence of elastic He-Li collisions on the steady-state Li atom number in the MOT is described, and the collision data are used to estimate the excitation efficiency of the discharge source. We also show that Penning collisions can be directly used to probe the temperature of the Li cloud without the need for an additional time-resolved absorption or fluorescence detection system.